Vertical silicon/silicon-germanium transistors with multiple threshold voltages

ABSTRACT

A method of forming vertical fin field effect transistors, including, forming a silicon-germanium cap layer on a substrate, forming at least four vertical fins and silicon-germanium caps from the silicon-germanium cap layer and the substrate, where at least two of the at least four vertical fins is in a first subset and at least two of the at least four vertical fins is in a second subset, forming a silicon-germanium doping layer on the plurality of vertical fins and silicon-germanium caps, removing the silicon-germanium doping layer from the at least two of the at least four vertical fins in the second subset, and removing the silicon-germanium cap from at least one of the at least two vertical fins in the first subset, and at least one of the at least two vertical fins in the second subset.

BACKGROUND Technical Field

The present invention generally relates to forming vertical transportfin field effect transistors (VT FinFETs) with multiple thresholdvoltages, and more particularly to forming VT FinFETs with differentgermanium concentration on the same substrate to provide thresholdvoltages.

Description of the Related Art

A Field Effect Transistor (FET) typically has a source, a channel, and adrain, where current flows from the source to the drain, and a gate thatcontrols the flow of current through the channel. Field EffectTransistors (FETs) can have a variety of different structures, forexample, FETs have been fabricated with the source, channel, and drainformed in the substrate material itself, where the current flowshorizontally (i.e., in the plane of the substrate), and FinFETs havebeen formed with the channel extending outward from the substrate, butwhere the current also flows horizontally from a source to a drain. Thechannel for the FinFET can be an upright slab of thin approximatelyrectangular Si, commonly referred to as the fin with a gate on the fin,as compared to a metal-oxide-semiconductor field effect transistor(MOSFET) with a gate parallel with the plane of the substrate.

Depending on the doping of the source and drain, an n-type FET (nFET) ora p-type FET (pFET) can be formed. An nFET and a pFET can be coupled toform a complementary metal oxide semiconductor (CMOS) device, where ap-channel MOSFET and n-channel MOSFET are coupled together.

With ever decreasing device dimensions, forming the individualcomponents and electrical contacts become more difficult. An approach istherefore needed that retains the positive aspects of traditional FETstructures, while overcoming the scaling issues created by formingsmaller device components, including channel lengths and gate dielectricthicknesses.

SUMMARY

In accordance with an embodiment of the present invention, a method offorming vertical fin field effect transistors is provided. The methodincludes forming a silicon-germanium cap layer on a substrate, andforming at least four vertical fins and silicon-germanium caps from thesilicon-germanium cap layer and the substrate, where at least two of theat least four vertical fins is in a first subset and at least two of theat least four vertical fins is in a second subset. The method furtherincludes forming a silicon-germanium doping layer on the plurality ofvertical fins and silicon-germanium caps. The method further includesremoving the silicon-germanium doping layer from the at least two of theat least four vertical fins in the second subset. The method furtherincludes removing the silicon-germanium cap from at least one of the atleast two vertical fins in the first subset and at least one of the atleast two vertical fins in the second subset.

In accordance with another embodiment of the present invention, a methodof forming vertical fin field effect transistors with differentthreshold voltages is provided. The method includes forming asilicon-germanium cap layer on a substrate, wherein thesilicon-germanium cap layer has a germanium concentration in the rangeof about 20 at. % to about 30 at. %. The method further includes formingat least four vertical fins and silicon-germanium caps from thesilicon-germanium cap layer and the substrate, wherein at least two ofthe at least four vertical fins is in a first subset and at least two ofthe at least four vertical fins is in a second subset. The methodfurther includes forming a silicon-germanium doping layer on theplurality of vertical fins and silicon-germanium caps, wherein thedoping layer has a higher germanium concentration than thesilicon-germanium cap layer. The method further includes removing thesilicon-germanium doping layer from the at least two vertical fins inthe second subset, and removing the silicon-germanium cap from at leastone of the at least two vertical fins in the first subset and at leastone of the at least two vertical fins in the second subset.

In accordance with yet another embodiment of the present invention, aplurality of vertical fin field effect transistors is provided. Theplurality of vertical fin field effect transistors includes at leastfour vertical fins on a substrate, wherein at least two of the at leastfour vertical fins is in a first subset and at least two of the at leastfour vertical fins is in a second subset, and wherein four of the atleast four vertical fins has a different germanium concentration fromthe other of the four vertical fins.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description will provide details of preferred embodimentswith reference to the following figures wherein:

FIG. 1 is a cross-sectional view showing a silicon-germanium cap layeron a substrate surface, in accordance with an embodiment of the presentinvention;

FIG. 2 is a cross-sectional view showing a silicon-germanium cap on eachof a plurality of vertical fins, in accordance with an embodiment of thepresent invention;

FIG. 3 is a cross-sectional view showing a doping layer on thesilicon-germanium caps and vertical fins, in accordance with anembodiment of the present invention;

FIG. 4 is a cross-sectional view showing a protective liner on thedoping layer, in accordance with an embodiment of the present invention;

FIG. 5 is a cross-sectional view showing a cover layer masking a subsetof the vertical fins in accordance with an embodiment of the presentinvention;

FIG. 6 is a cross-sectional view showing a subset of exposed verticalfins and silicon-germanium caps, in accordance with an embodiment of thepresent invention;

FIG. 7 is a cross-sectional view showing a mask and a fill layer, inaccordance with an embodiment of the present invention;

FIG. 8 is a cross-sectional view showing removal of predeterminedsilicon-germanium caps, in accordance with an embodiment of the presentinvention;

FIG. 9 is a cross-sectional view showing exposed vertical fins, inaccordance with an embodiment of the present invention;

FIG. 10 is a cross-sectional view showing the doping layer on a subsetof vertical fins, in accordance with an embodiment of the presentinvention;

FIG. 11 is a cross-sectional view showing a heat treatment to diffusegermanium into the vertical fins, in accordance with an embodiment ofthe present invention;

FIG. 12 is a cross-sectional view showing vertical fins with differentconcentrations of germanium, in accordance with an embodiment of thepresent invention;

FIG. 13 is a cross-sectional view showing an oxidation trim to adjustvertical fin thicknesses, in accordance with an embodiment of thepresent invention;

FIG. 14 is a cross-sectional view showing vertical fins with conformalthicknesses and varying germanium concentrations, in accordance with anembodiment of the present invention;

FIG. 15 is a cross-sectional view showing a planarization layer on thevertical fins, in accordance with an embodiment of the presentinvention;

FIG. 16 is a cross-sectional view showing vertical fin with a uniformheight, in accordance with an embodiment of the present invention;

FIG. 17 is a cross-sectional view showing gate structures on thevertical fins, in accordance with an embodiment of the presentinvention; and

FIG. 18 is a cross-sectional view showing vertical transport fin fieldeffect transistors, in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION

Embodiments of the present invention relate generally to controlling thethreshold voltage of vertical transport fin field effect transistors (VTFinFETs) by adjusting the concentration of germanium in the verticalfins forming the VT FinFET channels. The vertical fins can be intrinsicsilicon or silicon-germanium.

Embodiments of the present invention also relate generally to formingdifferent germanium sources on different vertical fins to control thefinal germanium concentrations in the vertical fins. Differentconfigurations of germanium sources with different germaniumconcentrations can be used as doping sources, where the types ofgermanium sources in contact with each vertical fin can determine thefinal germanium concentration.

Embodiments of the present invention also relate generally to heattreating a set of vertical fins on a substrate to cause germanium tomigrate from adjoining germanium sources into the vertical fins formingthe VT FinFET channels. The vertical fins can be heat treated until thegermanium concentration in each vertical fin reaches an equilibriumconcentration.

Exemplary applications/uses to which the present invention can beapplied include, but are not limited to: logic devices utilizing VTFinFETs.

It is to be understood that aspects of the present invention will bedescribed in terms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps can be varied within the scope of aspects of the presentinvention.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a silicon-germanium caplayer on a substrate surface is shown, in accordance with an embodimentof the present invention.

In one or more embodiments, a silicon-germanium cap layer 120 can beformed on the surface of a substrate 110, where the silicon-germaniumcap layer 120 can be epitaxially grown on the substrate. Thesilicon-germanium cap layer 120 can have a germanium concentration inthe range of about 10 at. % (atomic percent) to about 60 at. %, or inthe range of about 20 at. % (atomic percent) to about 30 at. %, or about25 at. %, although other concentrations are also contemplated. Thesilicon-germanium cap layer 120 can be can have a thickness in the rangeof about 3 nm to about 30 nm, or in the range of about 10 nm to about 30nm, or in the range of about 10 nm to about 20 nm, although otherthicknesses are also contemplated. The silicon-germanium cap layer 120can be used to form silicon-germanium caps.

In various embodiments, the substrate 110 can be a semiconductor waferor a wafer having a carrier layer, an insulating layer, and asemiconductor layer. In an embodiment, the substrate 110 can be a bulksilicon substrate (i.e., silicon wafer). In another embodiment, thesubstrate 110 can be a silicon-on-insulator (SOI) substrate.

FIG. 2 is a cross-sectional view showing a silicon-germanium cap on eachof a plurality of vertical fins, in accordance with an embodiment of thepresent invention.

In one or more embodiments, vertical fins 111 and silicon-germanium caps121 can be formed from the substrate 110 and silicon-germanium cap layer120, where the vertical fins 111 and silicon-germanium caps 121 can beetched from the substrate 110 and silicon-germanium cap layer 120. Adirectional etch (e.g., a reactive ion etch (RIE)) can be used to removematerial from the substrate. The vertical fins can each have the samewidth, height, and length.

In one or more embodiments, a plurality of vertical fins 111 can beformed by a sidewall image transfer (SIT) process, self-aligned doublepatterning (SADP) process, or self-aligned quadruple patterning (SAQP)process, to provide a tight pitch between vertical fins 111. ImmersionLithography can direct print down to about 78 nm pitch. Extremeultraviolet lithography (also known as EUV or EUVL), considered anext-generation lithography technology using an extreme ultraviolet(EUV) wavelength, can direct print down to a pitch smaller than 50 nm.Self-aligned double patterning (SADP) can achieve down to about 40 nm to60 nm fin pitch. Self-aligned quadruple patterning (SAQP) may be used togo down to below 40 nm fin pitch. While the figures illustrate adirect-write process, this is for descriptive purposes, since theseother processes are also contemplated, and the scope of the claims andinvention should not be limited to the particular illustrated features.

FIG. 3 is a cross-sectional view showing a doping layer on thesilicon-germanium caps and vertical fins, in accordance with anembodiment of the present invention.

In one or more embodiments, a doping layer 130 can be formed on thesilicon-germanium caps 121, vertical fins 111, and substrate surface.The doping layer 130 can be silicon-germanium (SiGe) having a highergermanium concentration than the silicon-germanium caps 121. In variousembodiments, the doping layer 130 can have a germanium (Ge)concentration in the range of about 10 at. % to about 65 at. %, or inthe range of about 35 at. % to about 65 at. %, or in the range of about45 at. % to about 55 at. %, or about 50 at. %, although otherconcentrations are also contemplated. The doping layer 130 can have athickness in the range of about 3 nm to about 10 nm, or in the range ofabout 5 nm to about 7 nm, although other thicknesses are contemplated.In various embodiments, the doping layer 130 can have a thickness thatis less than or equal to ⅓ the distance between the facing vertical finsidewalls, such that the two thicknesses of the doping layer 130 is lessthan ⅔ the distance between adjacent vertical fins, so the doping layer130 and protective liner 140 fit between adjacent vertical fins. Invarious embodiments, the distance between adjacent vertical fins 111 canbe in the range of about 15 nm to about 60 nm. The doping layer 130 canbe formed by a conformal deposition to control the thickness.

In various embodiments, the range of the Ge concentration of the dopinglayer 130 and the range of the Ge concentration of the silicon-germaniumcap layer 120 described above can be reversed, such that thesilicon-germanium caps 121 have a higher germanium concentration thanthe doping layer 130.

FIG. 4 is a cross-sectional view showing a protective liner on thedoping layer, in accordance with an embodiment of the present invention.

In one or more embodiments, a protective liner 140 on the doping layer130. The protective liner 140 can act as an etch stop to prevent removalof the doping layer 130. The protective liner 140 can be silicon nitride(SiN). The protective liner 140 can be formed by a conformal depositionto control the thickness.

FIG. 5 is a cross-sectional view showing a cover layer masking a subsetof the vertical fins in accordance with an embodiment of the presentinvention.

In one or more embodiments, a cover layer 150 can be formed on a portionof the substrate and vertical fins 111. The adjacent vertical fins 111covered by the cover layer 150 can form a first subset and the exposedadjacent vertical fins can form a second subset. The cover layer 150 canbe blanket deposited, and a predetermined portion of the cover layer 150removed to expose a predetermined subset of the vertical fins 111. Thecover layer 150 can be a flowable oxide or a polymeric material that canbe spun on.

FIG. 6 is a cross-sectional view showing a subset of exposed verticalfins and silicon-germanium caps, in accordance with an embodiment of thepresent invention.

In one or more embodiments, the protective liner 140 can be removed fromthe exposed vertical fins to uncover the doping layer 130, and thedoping layer can be removed to expose the vertical fins 111 andsilicon-germanium caps 121. The protective liner 140 and doping layer130 can be removed using selective etches. The exposed vertical fins canbe of the second subset. The protective liner 140 and doping layer 130can remain on the vertical fins of the first subset.

After removing the protective liner 140 and doping layer 130, the coverlayer 150 can be removed to expose the first subset of vertical fins111.

FIG. 7 is a cross-sectional view showing a mask and a fill layer, inaccordance with an embodiment of the present invention.

In one or more embodiments, a mask 170 and a fill layer 160 can beformed on the vertical fins 111 and substrate 110 to cover both thevertical fins 111 in the first subset and the vertical fins in thesecond subset. The fill layer 160 can be planarize by achemical-mechanical polishing (CMP) to expose the top surfaces of theprotective liner 140 on at least one vertical fin 111 in the firstsubset.

The mask 170 can be formed over one or more vertical fins of the firstsubset and one or more vertical fins of the second subset, such that atleast one vertical fin 111 of the first subset is adjacent to a verticalfin 111 of the second subset. A selective, directional etch can be usedto remove a portion of the protective liner 140 to expose the dopinglayer 130. The etch can remove a portion of the fill layer 160 aroundthe exposed vertical fin of the first subset and the exposed verticalfin of the second subset. Removal of the fill layer 160 around thevertical fin of the second subset can expose the silicon-germanium cap121. Another selective, directional etch can be used to remove thesilicon-germanium cap 121 exposed by removal of the protective liner 140to expose the top surface of the vertical fin 111. The selective etchcan also remove the exposed silicon-germanium cap 121 on the verticalfin in the second subset.

Removal of the silicon-germanium cap 121 from predetermined verticalfins 111, and removal of the doping layer 130 from predeterminedvertical fins can create a configuration of vertical fins havingdifferent germanium sources with different germanium concentrations ondifferent vertical fins. A vertical fin 111 can have no germaniumsource, only a silicon-germanium cap 121 having a predeterminedgermanium concentration, only a doping layer 130 with a predeterminedgermanium concentration, or both a silicon-germanium cap 121 and adoping layer 130. The different configurations of germanium sources canprovide for different germanium concentrations in the vertical fins 11after diffusion. The vertical fins 111 can be intrinsic silicon, or thevertical fin can include an n-type or a p-type dopant.

FIG. 8 is a cross-sectional view showing removal of predeterminedsilicon-germanium caps, in accordance with an embodiment of the presentinvention.

In one or more embodiments, the fill layer 160 and mask 170 can beremoved after removal of the silicon-germanium caps 121 to expose theprotective liner 140. The sidewalls of the vertical fins 111 of thesecond subset can be partially exposed. SiGe caps 121 can be removed bya selective etch, such as a wet etch process containing hydrogenperoxide (H₂O₂). Alternatively, SiGe caps can be removed by exposure togas phase hydrogen chloride (HCl).

FIG. 9 is a cross-sectional view showing exposed vertical fins, inaccordance with an embodiment of the present invention.

In one or more embodiments, the protective liner 140 can be removed toexpose the underlying doping layer 130.

FIG. 10 is a cross-sectional view showing the doping layer on a subsetof vertical fins, in accordance with an embodiment of the presentinvention.

In one or more embodiments, the protective liner 140 and a portion ofthe doping layer 130 extending above the vertical fin 111 can be removedto leave the doping layer on the sidewalls of the vertical fin.Selective isotropic etching can be used to remove the protective liner140.

FIG. 11 is a cross-sectional view showing a heat treatment to diffusegermanium into the vertical fins, in accordance with an embodiment ofthe present invention.

In one or more embodiments, a heat treatment can be used to diffuse thegermanium from the germanium sources into the adjoining vertical fins111 and substrate 110. The heat treatment can be at a suitabletemperature and for a sufficient time for the germanium concentration inthe vertical fins, doping layer 130 and silicon-germanium caps 121 toreach an equilibrium distribution in the vertical fins 111. Thesilicon-germanium of the doping layer 130 can diffuse into the surfaceof the substrate to form a bottom source/drain region 180. The heattreatment can be an annealing process at a temperature in the range ofabout 700° C. to about 1250° C., or in the range of about 800° C. toabout 1100° C. The heat treatment can be for a time in the range ofabout 1 second to about 3600 seconds, or in the range of about 30seconds to about 360 seconds.

In some embodiments, the annealing can be performed in vacuum. In someembodiments, the annealing is performed in an environment containingnitrogen, argon, helium, neon, hydrogen, oxygen, or any suitablecombination of those gases. If oxygen is present during annealing, theannealing process is sometimes referred to as condensation process. In acondensation process, oxygen preferably reacts with silicon in silicongermanium to form silicon oxide (SiO) and repelling germanium into thevertical fins 111, effectively increasing germanium concentration in thevertical fins 111. Other suitable annealing conditions are alsoconceived.

FIG. 12 is a cross-sectional view showing vertical fins with differentconcentrations of germanium, in accordance with an embodiment of thepresent invention.

In one or more embodiments, the doping layer 130 and the vertical fins111 can intermingle to cause the width of the vertical fins 111 toincrease. Similarly, a portion of the silicon-germanium caps 121 canintermingle causing the heights of the vertical fins to increase. Thevertical fins 111 can, thereby, have different dimensions after the heattreatment compared to the originally formed vertical fins 111. A portionof the germanium can migrate into the substrate to form a gradedsilicon-germanium bottom source/drain 182 below a silicon-germaniumvertical fin.

The amount of germanium diffused into the vertical fin can depend onboth the germanium concentration and the volume of the doping layer 130and silicon-germanium caps 121, wherein a thicker doping layer 130 orthicker silicon-germanium cap 121 can provide a larger reservoir ofgermanium for diffusion into the vertical fin 111. The Ge concentrationof a vertical fin can be related to the ratio of the volume of thevertical fin to the volume and germanium density of the germanium dopingsources (doping layer 130 and/or silicon-germanium caps 121).

A vertical fin 112 formed from heat treatment of only a doping layer 130can have a germanium concentration in the range of about 20 at. % toabout 40 at. %, or in the range of about 25 at. % to about 30 at. %. Thevertical fin 112 formed by diffusion of germanium from only a dopinglayer 130 can provide a threshold voltage, Vt₁, in the range of about250 mV to about 450 mV, where the threshold voltage, Vt₁, is for avertical fin field effect transistor fabricated with the vertical fin112.

A vertical fin 113 formed from heat treatment of a doping layer 130 anda silicon-germanium cap 121 can have a germanium concentration in therange of about 40 at. % to about 60 at. %, or in the range of about 40at. % to about 50 at. %, or about 50 at. % to about 60 at. %. Thevertical fin 113 formed by diffusion of germanium from both a dopinglayer 130 and a silicon-germanium cap 121 can provide a thresholdvoltage, Vt₂, in the range of about 50 mV to about 250 mV, or in therange of about 50 mV to about 150 mV, where the threshold voltage, Vt₂,is for a vertical fin field effect transistor fabricated with thevertical fin 113.

A vertical fin 114 formed from heat treatment of only asilicon-germanium cap 121 can have a germanium concentration in therange of about 5 at. % to about 30 at. %, or in the range of about 10at. % to about 20 at. %. The vertical fin 114 formed by diffusion ofgermanium from only a silicon-germanium cap 121 can provide a thresholdvoltage, Vt₃, in the range of about 300 mV to about 600 mV, or in therange of about 350 mV to about 550 mV, where the threshold voltage, Vt₃,is for a vertical fin field effect transistor fabricated with thevertical fin 114.

A vertical fin 115 not having either a doping layer 130 or asilicon-germanium cap 121 can have a germanium concentration of 0 at. %after heat treatment, or the germanium concentration of the substrate110. The vertical fin 115 can provide a threshold voltage, Vt, in therange of about 600 mV to about 650 mV, or a threshold voltage, Vt₄, of650 mV where the vertical fin has a germanium concentration of 0 at. %.Since vertical fin 115 does not have either a doping layer 130 or asilicon-germanium cap 121, heat treatment does not cause any Gediffusion into vertical fin 115. Each of the vertical fins 111 with agermanium concentration greater than the intrinsic silicon vertical fincan provide a lower threshold voltage, wherein the threshold voltage,Vt, can be in the range of about 50 mV to about 650 mV for a germaniumrange of about 60 at. % to about 0 at. %. The threshold voltage can varylinearly with the germanium concentration, where the threshold voltagecan change by 100 mV for each 10 at. % change in germaniumconcentration. An increase in Ge concentration decreases the thresholdvoltage, Vt. Induced strain in the vertical fins 111 can also cause anadjustment of the threshold voltage, Vt, where a total thresholdvoltage, Vt_(tot), can be the combination of the threshold voltage shiftdue to the germanium concentration and a threshold voltage shift due toa strain imparted to the vertical fin 111. The threshold voltage shiftdue to an imparted strain can be in the range of about 1 mV to about 50mV.

In various embodiments, the germanium concentration of vertical fin 114can be greater than the germanium concentration of vertical fin 112,where the Ge concentration of the silicon-germanium cap 121 is greaterthan the Ge concentration of the doping layer 130, where the Geconcentration and the volume of the silicon-germanium cap 121 provides agreater Ge reservoir than the concentration and volume of the dopinglayer 130.

In a non-limiting exemplary embodiment, a silicon-germanium cap 121 canbe formed on each of four fins, where the silicon-germanium cap 121 hasa Ge concentration of 25 at. %. A doping layer 130 can be formed on eachof four fins, where the doping layer 130 has a Ge concentration of 50at. %. After heat treatment, the vertical fins 111 can have a Geconcentration in the range of about 5 at. %. to about 60 at. %.

FIG. 13 is a cross-sectional view showing an oxidation trim to adjustvertical fin thicknesses, in accordance with an embodiment of thepresent invention.

In one or more embodiments, the vertical fins 111 can be partiallyoxidized to trim excess material, and return the vertical fins 111 tomore uniform dimensions. The vertical fins 111 can be exposed to anoxidizing atmosphere, where vertical fins having a higher germaniumconcentration are oxidized at a greater rate, so to a greater extent,than the vertical fins with a lower germanium concentration. Theoxidation can also force germanium into the vertical fins to increasethe remaining germanium concentration of the vertical fins 111. Theoxidation can form an oxide layer 190 on the outer surfaces of thevertical fins 111 and substrate, particularly where thesilicon-germanium formed bottom source/drain regions 180 at the surfaceof the substrate. The thickness of the oxide layer 190 can varydepending on the germanium concentration of the vertical fin, such thatthe thickness of the oxide layer 190 compensates for the difference inwidths of the vertical fins depending on the germanium concentration. Invarious embodiments, the oxidation can be performed as part of the heattreatment described above through a condensation process. The oxidationalso can be optional.

FIG. 14 is a cross-sectional view showing vertical fins with conformalthicknesses and varying germanium concentrations, in accordance with anembodiment of the present invention.

The oxide layer 190 can be removed from the outer surfaces of thevertical fins 111 and substrate 110 by a selective, isotropic etch.After removal of the oxide layer 190 the vertical fins 111 can have awidth in the range of about 5 nm to about 15 nm, although other widthsare contemplated.

FIG. 15 is a cross-sectional view showing a planarization layer on thevertical fins, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a planarization layer 200 can be formed onthe vertical fins 111, where the planarization layer 200 can be blanketdeposited, and cover the top surfaces of a plurality of vertical fins111. The planarization layer 200 can be a flowable oxide or a polymericmaterial. In various embodiments, the planarization can be optional.

FIG. 16 is a cross-sectional view showing vertical fin with a uniformheight, in accordance with an embodiment of the present invention.

In one or more embodiments, a chemical-mechanical polishing (CMP) can beused to reduce the heights of each of the vertical fins 111 and theplanarization layer 200 to a uniform height. In various embodiments, thevertical fins 111 can have a height in the range of about 20 nm to about100 nm after planarization, or in the range of about 30 nm to about 60nm, although other heights are also contemplated.

FIG. 17 is a cross-sectional view showing gate structures on thevertical fins, in accordance with an embodiment of the presentinvention.

In one or more embodiments, the planarization layer 200 can be removed,for example, by a selective etch, and a gate structure can be formed onthe exposed vertical fins 111. A bottom spacer layer 210 can be formedon the bottom source/drain regions 180, and bottom source/drain 182. Thebottom spacer layer 210 can be directionally deposited, and an isotropicetch used to thin the bottom spacer layer and remove material from thesidewalls of the vertical fins 112, 113, 114, 115. The bottom spacerlayer 210 can be an insulating dielectric material, for example, siliconoxide (SiO), silicon nitride (SiN), silicon borocarbonitride (SiBCN),silison oxycarbonitride (SiOCN), silicon oxycarbide (SiOC), siliconcarbonitride (SiCN), silicon boronitride (SiBN), a low-k dielectricmaterial, or a combination thereof.

A gate dielectric layer 220 can be formed on the bottom spacer layer 210and sidewalls of the vertical fins 112, 113, 114, 115, where the gatedielectric layer 220 can be formed by a conformal deposition. The gatedielectric layer 220 can be an insulating dielectric material, forexample, silicon oxide (SiO), silicon nitride (SiN), a high-k dielectricmaterial, or a combination thereof.

A conductive gate electrode 230 can be formed on the gate dielectriclayer 220, where the conductive gate electrode 230 can include aconductive gate fill and a work function layer between the conductivegate fill and the gate dielectric layer 220. The conductive gate fillcan be a conductive metal, for example, tungsten, and the work functionlayer can be a metal carbide or metal nitride. The gate dielectric layer220 and conductive gate electrode 230 form the gate structure on thevertical fins 112, 113, 114, 115.

A top spacer layer 240 can be formed on the gate structure toelectrically isolate the conductive gate electrode 230 from topsource/drains formed on the vertical fins. The top spacer layer can bedirectionally deposited and partially etched back. The top spacer layer240 can be an insulating dielectric material, for example, silicon oxide(SiO), silicon nitride (SiN), silicon borocarbonitride (SiBCN), silisonoxycarbonitride (SiOCN), silicon oxycarbide (SiOC), silicon carbonitride(SiCN), silicon boronitride (SiBN) a low-k dielectric material, or acombination thereof.

FIG. 18 is a cross-sectional view showing vertical transport fin fieldeffect transistors, in accordance with an embodiment of the presentinvention.

In one or more embodiments, top source/drains 250 can be formed on eachof the vertical fins 112, 113, 114, 115, where the top source/drains 250can be epitaxially grown on the vertical fins.

An interlayer dielectric (ILD) layer 260 can be formed on the top spacerlayer 240 and the top source/drains 250. The ILD layer 260 can besilicon oxide (SiO). In various embodiments, the ILD layer can include aliner (e.g., silicon nitride, not shown) before a silicon oxide (SiO)deposition.

In various embodiments, isolation regions 270 can be formed betweenadjacent vertical fins 112, 113, 114, 115 to electrically separate theVT FinFETs formed from each of the vertical fins. The isolation regions270 can be an insulating dielectric material, for example, silicon oxide(SiO), silicon nitride (SiN), silicon oxynitride (SiON), or any othersuitable dielectric materials or suitable combination of thosematerials. Each vertical fin 112, 113, 114, and 115 can form a separateVT FinFET.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present invention, as well as other variations thereof, means that aparticular feature, structure, characteristic, and so forth described inconnection with the embodiment is included in at least one embodiment ofthe present invention. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This may be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements can also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements can be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

Having described preferred embodiments of verticalsilicon/silicon-germanium transistors with multiple threshold voltagesand fabrication methods thereof (which are intended to be illustrativeand not limiting), it is noted that modifications and variations can bemade by persons skilled in the art in light of the above teachings. Itis therefore to be understood that changes may be made in the particularembodiments disclosed which are within the scope of the invention asoutlined by the appended claims. Having thus described aspects of theinvention, with the details and particularity required by the patentlaws, what is claimed and desired protected by Letters Patent is setforth in the appended claims.

What is claimed is:
 1. A method of forming vertical fin field effecttransistors, comprising: forming a silicon-germanium cap layer on asubstrate; forming at least four vertical fins and silicon-germaniumcaps from the silicon-germanium cap layer and the substrate, where atleast two of the at least four vertical fins is in a first subset and atleast two of the at least four vertical fins is in a second subset;forming a silicon-germanium doping layer on the plurality of verticalfins and silicon-germanium caps; removing the silicon-germanium dopinglayer from the at least two of the at least four vertical fins in thesecond subset; and removing the silicon-germanium cap from at least oneof the at least two vertical fins in the first subset, and at least oneof the at least two vertical fins in the second subset.
 2. The method ofclaim 1, further comprising, heat treating the at least four verticalfins, silicon-germanium caps, and silicon-germanium doping layer todiffuse germanium into at least three of the at least four vertical finsand substrate.
 3. The method of claim 2, wherein the germaniumconcentration is different between each of the at least two of the atleast four vertical fins in a first subset and each of the at least twoof the at least four vertical fins in a second subset.
 4. The method ofclaim 3, wherein the germanium concentration in one of the at least twovertical fins in the first subset is in the range of about 20 at. % toabout 60 at. %.
 5. The method of claim 3, wherein the germaniumconcentration in one of the at least two vertical fins in the secondsubset is in the range of about 0 at. % to about 30 at. %.
 6. The methodof claim 2, wherein the germanium diffused into the substrate forms abottom source/drain region below the at least two vertical fins in thefirst subset.
 7. The method of claim 6, further comprising, performingan oxidation trim on the plurality of vertical fins and bottomsource/drain region.
 8. The method of claim 7, wherein the plurality ofvertical fins have a width in the range of about 3 nm to about 10 nmafter the oxidation trim.
 9. The method of claim 7, further comprisingplanarizing the plurality of vertical fins to have a uniform height onthe substrate.
 10. A method of forming vertical fin field effecttransistors with different threshold voltages, comprising: forming asilicon-germanium cap layer on a substrate, wherein thesilicon-germanium cap layer has a germanium concentration in the rangeof about 20 at. % to about 30 at. %; forming at least four vertical finsand silicon-germanium caps from the silicon-germanium cap layer and thesubstrate, wherein at least two of the at least four vertical fins is ina first subset and at least two of the at least four vertical fins is ina second subset; forming a silicon-germanium doping layer on theplurality of vertical fins and silicon-germanium caps, wherein thedoping layer has a higher germanium concentration than thesilicon-germanium cap layer; removing the silicon-germanium doping layerfrom the at least two vertical fins in the second subset; and removingthe silicon-germanium cap from at least one of the at least two verticalfins in the first subset, and at least one of the at least two verticalfins in the second subset.
 11. The method of claim 10, furthercomprising, forming a protective liner on the silicon-germanium dopinglayer, and removing the protective liner from the silicon-germaniumdoping layer for the at least two vertical fins in the second subset.12. The method of claim 10, wherein the silicon-germanium doping layerhas a germanium concentration in the range of about 35 at. % to about 65at. %.
 13. The method of claim 10, further comprising, heat treating theat least four vertical fins, silicon-germanium caps, andsilicon-germanium doping layer to diffuse germanium into the verticalfins and substrate.
 14. The method of claim 13, wherein at least one ofthe at least two vertical fins in the first subset provides a thresholdvoltage in the range of about 100 mV to about 250 mV.
 15. The method ofclaim 13, wherein at least one of the at least two vertical fins in thesecond subset provides a threshold voltage in the range of about 250 mVto about 500 mV.